The present invention generally relates to the production and design of ink cartridge units, and more particularly to an ink cartridge system having a high-durability printhead which includes an orifice plate structure fixedly secured to the printhead in an effective and permanent manner. The printhead is likewise characterized by improved levels of abrasion resistance and corrosion avoidance.
Substantial developments have been made in the field of electronic printing technology. A wide variety of highly-efficient printing systems currently exist which are capable of dispensing ink in a rapid and accurate manner. Thermal inkjet systems are especially important in this regard. Printing units using thermal inkjet technology basically involve a cartridge which includes at least one ink reservoir chamber in fluid communication with a substrate (preferably made of silicon) having a plurality of thin-film heating resistors thereon. Selective activation of the resistors causes thermal excitation of the ink materials retained inside the ink cartridge and expulsion thereof from the cartridge. Representative thermal inkjet systems are discussed in U.S. Pat. Nos. 4,500,895 to Buck et al.; 4,794,409 to Cowger et al.; 4,509,062 to Low et al.; 4,929,969 to Morris; 4,771,295 to Baker et al.; 5,278,584 to Keefe et al.; and the Hewlett-Packard Journal, Vol. 39, No. 4 (August 1988), all of which are incorporated herein by reference.
Another important component employed in thermal inkjet printing systems of the type described above (and in other ink cartridge systems using different ink expulsion systems aside from thin-film heating resistors) involves a structure known as an "orifice plate" which is also conventionally characterized as a "nozzle plate". The orifice plate is normally secured to the top portions of the printhead (e.g. above the ink expulsion components). To permit ink ejection from the orifice plate, the plate typically includes a number of openings or "orifices" passing entirely therethrough. Each of these orifices will have a representative diameter of about 0.01-0.05 mm, although this parameter may be varied as needed in accordance with the particular ink cartridge system under consideration. In a thermal inkjet printing system which employs a plurality of heating resistors to eject ink from the cartridge, each one of the openings in the orifice plate is typically in substantial alignment and registry with at least one of the thin film resistors in the printhead so that ink materials which are thermally excited (e.g. heated) during use of the ink cartridge can pass out of the printhead and orifice plate for delivery to a selected print media composition (preferably paper).
Many different materials have been used to produce the orifice plate in an ink cartridge system. For example, in conventional systems, representative and preferred materials suitable for fabricating the orifice plate include a rigid internal support member manufactured from, for example, elemental nickel (Ni), palladium/nickel alloys [Pd/Ni], any other rigid, electroformable metals with engineerable properties, or non-electroformed materials such as steel, rigid plastic, or micromachined metal sheets. This support member made from these materials is thereafter coated on both sides (e.g. top and bottom), along the outer peripheral edges thereof, and within the orifices with a protective metallic outer coating. Representative metallic coating compositions suitable for this purpose typically include elemental platinum (Pt), elemental palladium (Pd), elemental gold (Au), and mixtures thereof, with these metals being designated herein as "noble metals". In the alternative, the orifice plate may be constructed from a single metal composition (compared with the multi-component system listed above) configured in the shape of a flat panel member, with this structure being produced from one or more of the previously-described noble metals (e.g. elemental platinum (Pt), elemental palladium (Pd), elemental gold (Au), and mixtures thereof.)
The orifice plate in an ink cartridge unit provides a number of important functions. For example, the orifice plate is designed to (1) protect the underlying components in the printhead including the ink ejectors [e.g. the thin-film resistors in a thermal inkjet printing system] from abrasion and other physical damage; (2) properly direct the flow of ink from the cartridge to a selected print media material [e.g. paper] in a cohesive, accurate, and controlled manner; and (3) provide a protective outer barrier which is used to control the corrosive effects of ink compositions which, depending on the ink product under consideration, can cause additional damage to the underlying printhead components. However, all of these important goals cannot be effectively achieved unless the orifice plate is fixedly secured to the printhead in a non-detachable manner so that it remains an integral and permanent part of the printhead. Premature disengagement or displacement of the orifice plate from the printhead will prevent the printhead (and cartridge unit) from properly functioning. It will then be necessary to discard the ink cartridge (and attached printhead) which is disadvantageous from an economic and practical standpoint.
Premature orifice plate detachment and/or misalignment typically occurs in accordance with the metallic character thereof (e.g. the use of gold, platinum, palladium, and the like), and the difficulties which may be encountered in adhering this type of orifice plate in position to the underlying printhead components. In a conventional and representative ink cartridge printhead (e.g. of the thermal inkjet variety) which will be discussed in substantial detail below, an underlying "substrate" is provided as previously noted which is typically manufactured from silicon. The operating components of the printhead (e.g. the "ink ejectors" which shall collectively involve the various components used to expel ink from the cartridge unit) are typically positioned directly on the substrate, along with the necessary conductive circuit elements (otherwise known as "traces") associated with the ink ejectors. In a thermal inkjet system, the ink ejectors will comprise a plurality of thin film resistors that are preferably made from a tantalum-aluminum composition known in the art for resistor fabrication. Again, further information concerning the substrate and various components which may be located thereon will be outlined below. Positioned on top of the substrate is an intermediate layer of barrier material (e.g. conventionally known as a "barrier layer") which performs many important functions. The barrier layer covers the conductive traces/circuit elements on the surface of the substrate, but is located between and around the ink ejectors (heating resistors) without covering them. As a result, ink expulsion chambers are formed directly above each ink ejector. In a thermal inkjet system, the ink expulsion chambers are typically characterized as "ink vaporization chambers". Within the individual ink expulsion chambers, ink materials are subjected to the necessary physical processes which enable them to be ejected from the cartridge unit. In a thermal inkjet system, ink materials are heated, vaporized, and subsequently expelled from the ink vaporization chambers through the orifices of the orifice plate.
The barrier layer is traditionally produced from conventional organic compounds [e.g. epoxies, acrylates, and epoxy-acrylate mixtures], photoresist materials, or other similar compositions as outlined in U.S. Pat. Nos. 4,794,410; 4,937,172; 5,198,834; and 5,278,485 which are incorporated herein by reference. Furthermore, the barrier layer is applied to the substrate using conventional processing methods including but not limited to standard photolithographic techniques which are known in the art for this purpose. More specific information regarding representative compositions (e.g. organic compounds) which may be used to produce the barrier layer will likewise be discussed in considerable detail below. In addition to clearly defining the ink expulsion/vaporization chambers in the printhead, the barrier layer performs a number of other important functions including (1) electrical and chemical insulation of the underlying substrate and circuit traces thereon; and (2) enhancement of the overall strength and structural integrity of the entire printhead by imparting an additional degree of rigidity to the structure.
To complete the printhead manufacturing process, the orifice plate is thereafter placed on top of the barrier layer in a manner which allows substantial registry of the openings/orifices through the orifice plate with the underlying ink expulsion/vaporization chambers and ink ejectors (e.g. the thin-film resistors in a thermal inkjet printing system.) To ensure accurate ink delivery and maintain overall cartridge structural integrity, the orifice plate must be fixedly secured to the barrier layer in a non-detachable manner as discussed above. Otherwise, if secure attachment of these components does not take place, a number of problems can occur including (A) misdirected ink expulsion which will typically result in improperly printed images; (B) decreased cartridge life caused by the premature displacement of the orifice plate from the remainder of the printhead; and (C) diminished resistance of the printhead and its internal components to chemical (ink-based) deterioration which can more readily occur when the structural integrity of the printhead is compromised. Again, these problems will often result when the above-listed metals (especially palladium) are used in connection with the orifice plate. Secure adhesion of these materials to the organic compositions which are typically employed to manufacture the barrier layer has traditionally presented a number of difficult problems as previously noted.
A variety of different methods have been implemented in order to secure the orifice plate to the barrier layer. These methods include but are not limited to the use of a separate layer between the orifice plate and barrier layer which contains one or more compositions that are designed to adhere these components together. Representative materials previously used for this purpose involve a number of chemical products including but not limited to uncured poly-isoprene photoresist which is applied using standard photolithographic and other known methods as discussed in U.S. Pat. No. 5,278,584 (incorporated by reference). Likewise, the use of photoresist materials for this purpose is discussed in U.S. Pat. No. 5,198,834 which is also incorporated by reference. U.S. Pat. No. 5,198,834 describes the application of a photoresist composition sold under the name "Waycoat SC Resist 900" (Catalog No. 839167) by Olin Hunt Specialty Products, Inc. which is a subsidiary of the Olin Corporation of West Paterson, N.J. (USA). This composition is diluted with a product known as "Waycoat PF Developer" (Catalog No. 840017) and thereafter developed using "Waycoat Negative Resist Developer" (Catalog No. 837773), with both of these materials likewise being sold by Olin Hunt Specialty Products, Inc. as previously noted. Other materials which have been employed as adhesive compounds to attach the orifice plate to the barrier layer include but are not limited to polyacrylic acid, as well as acrylate and epoxy-based adhesives.
Notwithstanding the developments listed above, a need remains for (1) a printhead which avoids premature orifice plate detachment and/or misalignment that is caused by incomplete adhesion of the orifice plate to the underlying material layers (e.g. the organic compound-based barrier layer); and (2) a method which enables secure and permanent affixation of the orifice plate to the underlying barrier layer in a printhead. Furthermore, it is important that the completed printhead be substantially abrasion resistant and capable of avoiding the corrosive effects of ink materials which are typically used in conventional printing systems. Unless these problems are avoided, the resulting printhead will be subject to premature failure and/or progressively diminished print quality. The present invention involves a unique printhead design and production method which are capable of preventing the difficulties described above. Not only do the materials and methods of the invention avoid problems associated with premature orifice plate detachment, but likewise provide superior levels of corrosion/abrasion resistance. As a result, the overall life of the entire ink cartridge is substantially prolonged, along with the maintenance of high print quality levels. All of these benefits and advantages will become readily apparent from the specific description of the invention set forth below which represents a significant advance in the art of ink cartridge technology.